Yup, Billy/Sim's method is lofted/laid out full scale. So they (can be) fully prefabricated on the ground and lifted up as a unit.

And easiest way to frame is boatbuilding-style, with ribs. Mainly because the sheathing works far better. In contrast, winging it with stick framing with rafters is easy, but then sheathing that surface is ridiculous. Especially with plywood.